In automotive technology, the process of testing is often carried out in such a way that real components, such as for example real internal combustion engines, real tyres, real transmissions, real batteries, real steering systems, real power trains, real vehicles etc. are arranged on test beds. This real component to be tested frequently also determines the name of the test bed. Thus, one speaks of engine test beds, tyre test beds, transmission test beds, vehicle test beds etc. These test beds allow for example the development of internal combustion engines, of vehicle components or the detection of errors in networked vehicle control units, which may have an effect on the overall behaviour of the vehicle. The testing is here a process that is used to obtain greater certainty as to whether technical objects, technical systems or technical products and processes, the real component or the virtual component, operate within certain boundary conditions and/or whether certain characteristics and/or requirements are met. Tests carried out therefore always simulate or anticipate real processes in simulated environments. In the most general case, the simulated environment exchanges with the tested real component material flows (e.g. a media flow such as oil, water etc.), energy flows (e.g. electric current/voltage, rotary speed/torque etc.) and information flows (e.g. measured data etc.) and in this way allows technical processes to be examined without requiring, affecting or compromising the future real environment of the real component. Therefore, a test result will never be perfectly valid, but will always be an approximation. The quality of the approximation depends, inter alia, on the quality of the simulated environment and on the quality that can be achieved when simulating the exchange of energy, information and material flows that occur in the real world. This simulated environment will be referred to below as a virtual component. The real component and the virtual component will jointly be referred to as a test object. The test object and the test bed are also frequently jointly referred to as Hardware-In-The-Loop-System (HiL System) or more specifically as “X-In-The-Loop-System,” wherein X denotes the respective test object.
A virtual component consists of simulation models which are substantially implemented as software with implemented algorithms as well as mathematical or physical models, which are run on a simulation unit, generally a computer.
Also for carrying out the test, actuators (a number of actuators) and sensors (a number of sensors) will normally be present on the test bed, as well as possibly a flow control (e.g. a test bed control unit, an automation unit etc.) and periphery (such as e.g. a data logger etc.). The sensors measure physical, chemical or information-related states or state changes (“measured variables”) of the real component and the actuators impose certain chemical, physical or Information-related states or state changes (“set points”) on the real components. Actuators are therefore the signal conversion counter-piece of sensors. Actuators and sensors link the real world with the virtual world of the test object, i.e. the real component and the virtual component. Examples of actuators are electric, pneumatic or hydraulic load units for imposing rotary speeds, torques, velocities or distances, controllable electrical resistors, oil conditioning systems, air conditioning systems etc. Examples of sensors are torque sensors and rotary encoders.
The real component, the virtual component, actuators and sensors are dynamic systems with certain response behaviour. Thus, also a Hardware-In-The-Loop-System is, as an interconnection of these components, a dynamic system.
An example of a test is a virtual test drive of a hybrid vehicle (internal combustion engine and electric motor) along the Großglockner High Alpine Road under a realistic simulation of humidity, air temperature, rotary speed and torque behaviour of the real component “internal combustion engine,” which is arranged on an engine test bed. It is assumed that the aim of this test drive is the evaluation of the dynamic behaviour of the electric motor as well as the temperature behaviour of the traction battery, which are simulated as a virtual component, for a certain type of driver, e.g. a sporty driver with an aggressive gear-changing behaviour. The test route (here the Großglockner High Alpine Road), the driving behaviour as well as the driving environment are also simulated. During this test drive, the Hardware-In-The-Loop-System is set into vibration by the unevenness of the road, by gusts of wind, by the driver's braking and steering activities and/or by combustion shocks. However, these vibrations will probably not be exactly identical with the vibrations occurring during a real drive with the hybrid vehicle over the Großglockner High Alpine Road, due to the dynamic behaviour of the sensors and actuators and due to the simulation accuracy of the virtual component, which is always limited on account of it being a simulation.
Another example is shown in EP 1 037 030 B1, which discloses a method for simulating the behaviour of a vehicle on a road on a power train test bed, wherein a vehicle model and a tyre model (virtual components) are used for the simulation.
In practice, the virtual components are often retrofitted to existing test bed infrastructures. In this way, a conventional, traditional test bed, which so far could impose only simple set point profiles, becomes an efficient X-In-The-Loop test environment, which allows the implementation of new test tasks, such as for example the above-described drive on the Großglockner High Alpine Road under different boundary conditions. The existing test bed actuators and test bed sensors with their underlying dynamic subsystems and control structures are often supposed to remain unchanged (e.g. for cost reasons) or are unknown to the supplier of the virtual component. The same virtual component is often also used on different test beds with different dynamic response behaviours or on different test bed types. It also occurs that a virtual component is replaced with another virtual component (e.g. with modified models).
A further problem in connection with such virtual components can develop on a test bed if the virtual components are to represent extreme load cases that reach or exceed the limits of the implemented actuators, sensors or the real component.
Due to the dynamic response behaviour of the actuators and sensors integrated in the test bed, but also due to the interferences that are always present in the available measurements (e.g. measurement noise, limited resolution etc.), frequently undesired, unexpected and unrealistic vibration and resonance phenomena of the dynamic overall system occur, which can have a negative influence on the test results and may in an extreme case cause the use of the virtual components to fail altogether.
Conventionally, this scenario could be counteracted by using filters (e.g. Bessel filters, Butterworth filters, etc.) for attenuating vibrations which, however, limits the available dynamics of the test bed, which is not desired. In this case, it would no longer be possible to carry out test situations with strong dynamics, e.g. a very rapid change of rotary speeds or torques. A further important negative characteristic that occurs if such filters are used is the distortion of important dynamic states during testing. As an example, the angular momentum on mechanical/rotatory test beds (e.g. power train) could be mentioned, which is exchanged between the real and the virtual component. The use of filters causes here the real applied rotary momentum (e.g. from the internal combustion engine) to be incorrectly introduced into the virtual component, which consequently leads to incorrect test results (e.g. an excessively high/excessively low fuel consumption). Filters moreover also always cause a phase shift which, inter alia, has a negative influence on the stability reserve of the HiL system.